secondary air valve opening
Contents
1. P P l b Fig 8 Accelerator pump is built into cover PLUNGER SHAFT REMOVES VALVE The intake check valve assembly fits tightly into the bottom of the pump cylinder and can be re moved by tapping lightly on the end of the pump plunger shaft Tap the plunger end carefully to guard against damage to the shaft guide lugs cast into the bowl cover es 25 Fig 9 Tap shaft end to remove check valve PUMP LINK CONTROLS TRAVEL Because less pump output is needed at higher speeds in TorqueFlite equipped models the pump plunger S link angles outward at its center so the link can move over center This arrangement re duces plunger travel when the throttle is in the higher speed range 2 4 t Fig 10 Over center action cuts plunger travel SOME MODELS NEED MORE OUTPUT Full pump output must be available longer for smooth acceleration of manual transmission models so a two stage linkage with a pump stroke pickup lever is used This model requires two sepa rate accelerator pump adjustments which must be made in sequence PICK UP LEVER Fig 11 Staged pump for manual shift models Fig 12 Wrong link position can cause hangup INSTALL S LINK PROPERLY Because the accelerator pump plunger link is angled for over center operation there is a wrong way and a correct way to install it The link will go on either way but can hang up over center if the top part of the S points2. MASTER TECHNICIANS SERVICE CONFERENCE THE 72 THERMO GUAD CARBURETOR lt d CHRYSLER P TH DODGE CHRYSL IMPERIAL DO E TRUCK nr SE s His m TS Va MOTORS CORPORATION Remember the first carburetor you took apart Maybe you worried about getting all those parts back where they belonged or the adjustments had you confused But then with an understanding of basic systems plus a look at the Service Manual the next job went easier and it all became routine It s still that way with new model carburetors even for some experienced technicians But it s not like starting over at the beginning in spite of changes in carburetor appearance and added refinements be cause underneath it all the same basic systems are still there Following Tech s advice we re going to assume that the basics of four barrel carburetor operation are generally understood as we cover the Thermo Quad carburetor used on some of our 72 models For orientation the differences from earlier more familiar carburetors are described first followed by the adjustments and some helpful servicing hints THERMO QUAD FEATURES nnn Choke Diaphragm Operation e eee Accelerator Pump Operation e ne Step Up Piston and Metering Rods THERMO QUAD ADJUSTMENTS Secondary Throttle Link e eere Air Valve Spring Tension eee Air Valve Openingecccrccccnvccevccescovvens Accelerator Pump
3. into position to open the valves Fig 16 Measure primary valve opening Slowly open the primary throttle valves the speci fied distance from the throttle bore walls At this point the secondary throttle valves should just be gin to open To adjust the setting bend the throttle link carefully at the angle Be sure to sup port the link while bending so the connecting levers will not be distorted The secondary air valve opening adjustment comes next in the sequence but can be made separately First make sure that the air valve is aligned when closed with the valve edges parallel with the inner walls of the valve opening in the fuel bowl cover AIR VALVE OPENING ADJUSTMENT VALVE EDGES PARALLEL WITH WALLS Fig 17 Valve must be aligned in opening Next open the air valve against its stop and check for the specified gap between the valve edge and the outer wall of the primary air horn section Bend the notched corner section of the air valve to adjust the opening if needed SECONDARY AIR VALVE OPENING AO Po ORNER es CHECK GAP BETWEEN 2 T VALVE AND Fig 18 Hold v valve m rom to p ah ci opening t Valve Spring Tensiam The secondary air valve spring tension adjustment follows the valve opening adjustment and can also be made separately To begin you first loosen the hollow spring adjuster lock plug with the special C 4152 tool This releases the spring windup tension and allows the ai
4. inward instead of out The correct installation is shown in an accompany ing illustration Step Up Piston and Metering Rods In the Thermo Quad primary metering section the two metering rods are yoked to a single step up piston which rides in a cylinder in the bowl cover casting As mentioned earlier the primary jets which work with the metering rods are located in the plastic fuel bowl M gt Fig 13 Single piston operates metering rods wh k z CAM AND LEVER RAISE LIFT ROD For its mechanical operation the step up piston has a lift rod which extends down through a pas sage in the fuel bowl into the throttle body The bottom end of the rod rides on a lever operated by a cam on the primary throttle shaft LIFTING ACTION FOLLOWS THROTTLE In the low and medium speed range the cam and lever lift the step up piston and metering rods in proportion to the primary throttle valve opening This action provides positive mixture control re gardless of variations in engine vacuum Fig 15 Cam provides positive mixture control VACUUM BALANCES SPRING FORCE As the secondary throttle valves open the step up piston operates the metering rods in the conven tional manner Vacuum on the piston balances against spring force to position the metering rods and vary the mixture as reguired by changes in operating conditions TAMPERING IS A NO NO The length of the step up piston lift rod is factory adjusted o
5. Stroke esee Choke Control Lever eee eee orn Diaphragm Connector Rod eee Vacuum KiCiCu asuwwascas vs r6 s vale ben on Fast Idle Cam and Linkage 2 10 Choke Unloade s d s s o abo sada soori anc i 10 Secondary Throttle Pick Up Lever 1l Fast die Speeds eska na s vel b a akne causal Gurb ldle Speed u ls s TE neesmu ava I Bowl Vent Valve eee eror 12 Float Height Setting 2 222 12 THERMO QUAD SERVICING HINTS 13 ODONNNOO OU INO THERMO GUAD FEATURES As suggested by the name the unigue feature of the Thermo Quad carburetor is its lower operating temperature which results mainly from the insulat ing properties of the molded plastic fuel bowl and the suspended design of the fuel metering sys tem Tests show that the Thermo Quad runs as much as 20 cooler than all metal carburetors FUEL BOWL CUTS HEAT CONDUCTION The plastic fuel bowl reduces engine heat conduc tion both to the fuel in the bowl and to the meter ing system built into the bowl cover The metering system parts extend down into the fuel bowl and except for the linkage and bowl cover screws there is essentially no metal to metal contact to transfer heat from the engine manifold to the fuel in the bowl or to the bowl cover metering parts LESS HEAT IMPROVES PERFORMANCE Important advantages are gained by holding car buretor and fuel temperatures down For exa
6. cuum Kick If you check the vacuum kick with the carburetor off the engine first open the throttle so you can move the choke and fast idle linkage to the closed position Then release the throttle to trap the fast idle cam in closed position The choke diaphragm stem of course must be fully retracted ON ENGINE ADJUSTMENT The same preliminary procedure can be used on the engine if you use an external vacuum source However when engine vacuum is used you back off the fast idle speed screw until the choke can be closed to the kick position at curb idle with the idle speed solenoid core fully extended Note the number of turns backed off so you can restore the setting afterward VACUUM KICK ADJUSTMENT me 0 g BACK OFF SCREW UNTIL CHOKE CAN GLOSI M Fig 24 Modulating spring must be extended EXTEND MODULATING SPRING With the choke diaphragm stem retracted apply light closing force on the choke control lever to extend the modulating spring and move the choke valve to the kick position Use a specified drill or gauge to measure the kick opening sy A 771 x BEND TANG ON a ADJUSTING LEVER BIT Fig 25 Tang position determines kick opening ADJUST FOR SLIGHT DRAG You should be able to feel a slight drag when the drill or gauge is removed To open or close the kick setting bend the tang on the choke adjusting lever PREVENT LEVER DISTORTION The choke adjusting lever must be supported while th
7. e tang is bent or the choke control lever adjust ment may be disturbed For support insert a screwdriver blade end in the U shaped opening Fig 26 Support lever when bending tang between the adjusting lever and the choke counter shaft which passes through it Fast Idle Cam and Linkage The next step in the Thermo Quad adjustment sequence is the fast idle cam and linkage setting To begin this adjustment you first position the fast idle operating lever by putting the fast idle speed adjusting screw on the second step and against the shoulder of the first step of the cam FAST IDLE CAM AND LINKAGE ADJUSTMENT Fig 27 Position cam before adjustment ACE 1 S d n x S m na a FT A fall if Fri 8 TRI With light ciae force on rM choke control lever the choke valve must open the specified amount AND LINKAGE ADJUSTMENT is E IKT ara FORCE on CONTROL pil itf SPECIFIEL m es AT 4 l t WEN DU o LE FAST iDL SCREW BEN FAST TIE ON 2nd STEP AGAINST CONNECTORS OD SHOULDER OF 1st STEP r M Mi a d sana ES S a m Fig 28 Gauge should withdraw with slight dag measured between the lower edge of the choke valve and the air horn wall To adjust the valve opening you bend the fast idle connector rod at the angle Choke Unloader After the fast idle cam and linkage setting the choke unloader adjustment is next Since the un loader opera
8. engine should be warmed up and the basic ignition timing correctly set before you adjust the fast idle speed POSITION SCREW ON CAM First with the engine stopped open the throttle slightly to allow the fast idle cam to engage the speed adjusting screw Move the choke valve closed so the speed adjusting screw is positioned on the second step of the cam against the shoulder of the first step Fig 31 Warm up engine before adjusting speed RETAIN CAM POSITION Start the engine without disturbing the position of the speed screw on the fast idle cam and allow en gine speed to settle down Adjust the screw to get the specified speed and then cycle the fast idle speed screw on and off the cam to double check the adjustment Curb ldlo Speed The next adjustment combines two settings curb idle speed and the throttle stop screw otherwise known as the slow curb idle speed screw Since the tie in between idle speed and mixture adjustments is generally understood we ll skip the mixture ad justment details here USTMI MENT THROTTLE STO SOLENOID MUST BE ENERGIZED You adjust the curb idle speed with the engine warmed up and running Snap the throttle to make sure that the curb idle solenoid core is fully ex tended and adjust the idle screw to get the speci fied speed FINISH WITH STOP SETTING With the engine running at curb idle speed and the solenoid core extended turn the throttle stop screw in until it j
9. etting with throttle valves closed throttle connector rod is in the specified hole in the pump arm CLOSE THROTTLE VALVES COMPLETELY Apply light force on the throttle lever to hold the primary throttle valves closed Measure the dis tance from the top of the plunger shaft to the top of the bowl cover If this dimension does not meet the specifications bend the throttle connector rod at the angle to correct y Fig 21 Pickup arm on manual shift models only MANUAL SHIFT ADDS A STEP On manual transmission carburetors you continue beyond the basic pump stroke setting by opening the throttle slowly until the secondary throttle shaft begins to move Hold this position and again measure the stroke as before If adjustment is need ed bend the pickup arm on the primary throttle shaft dog m Choke Control Lever To check the choke control lever setting with the carburetor on the engine you first remove the stainless steel choke well from the manifold so you can use the top surface of the well opening as a reference point for the measurement ESTABLISH A REFERENCE POINT When checking with the carburetor off the engine you set the carburetor base down on a flat surface which extends the base or flange line out under the choke control lever This provides the lower refer ence point for the measurement CHOKE CONTROL LEVER Fig 22 Hold measuring scale vertical MEASURE VERTICAL DISTANCE To check t
10. ferent tension rating and is a plain metal color Interchanging these springs will upset the basic choke calibration and can cause cold start stalling Overstretching the spring can also upset the choke kick operation The modulating spring can be unhooked accidentally and lost so keep an eye on it v M A AA gt PINS CAN SLIDE OUT When you install the bowl cover assembly make sure that the float lever pins are in correct position If a displaced float pin is trapped between the gasket surfaces when the bowl cover screws are tightened the bowl wall may crack Also note that the nozzle well O rings can produce a slight sepa ration between the bowl and bowl cover until they are compressed by tightening the cover screws m nn oo lt FLOAT PIN EL t TRAPPED BETWEEN GASKET SURFACES a j V i X j ark R a ll pt 1 i 1 A U A WR M m j 1 j LUE A 4 st Ses fa b 267 Va v Fig 36 Float pin can slip out of position VALVE SCREWS MUST BE SECURE If you loosen or remove air choke or throttle valve screws secure them after retightening to pre vent them from loosening under vibration and dropping out Even though these screws are small they can seriously damage the engine if drawn in Upset the screw ends with plier pressure or use support so you can peen the screw ends without bending the shafts HANDLE WITH CARE Be careful when you remove or install the air clean er to pre
11. he choke control lever setting on or off the car open the throttle slightly to free the fast idle linkage and push on the choke control lever to hold the choke valve closed Then check the verti cal distance between the top of the hole in the lever and the lower reference surface To adjust the setting carefully bend the choke connecting rod at the angle Diaphragm Connector Rod After checking the choke control lever setting we move on to the choke diaphragm For the choke diaphragm connector rod adjustment and the vac uum kick adjustment which follows the choke dia phragm stem must be fully retracted by engine vac uum or by vacuum from an external source ROD DOES NOT SET VACUUM KICK Unlike other carburetors the Thermo Quad choke diaphragm connector rod adjustment determines the secondary air valve closing gap instead of set ting the vacuum kick You begin the connector rod check with the diaphragm stem retracted and the air valve in closed position Ve why xc WIDTTTHTT M A ROD ADJUSTMENT uo Ha nt a ES oon De Ph AN vH TS ra Ar 7 WE ANUS Ste et pe BEAN ADD AT ANGLE ol 2 Se A Fig 23 Rod length determines valve position STOP IS IN CASTING Check for the specified clearance between the sec ondary air valve lip and its closing stop on the bowl cover casting If adjustment is needed bend the choke diaphragm connector rod at the angle Va
12. ide of the carburetor This port is closed by the secondary VACUUM DROP IN DIAPHRAGM IS SLOWED BY RESTRICTIONS Fig 6 Restrictions slow vacuum bleed off throttle valve and does not affect diaphragm vacuum as long as the valve is closed DIAPHRAGM VACUUM DROPS SLOWLY When the secondary throttle valves open manifold vacuum drops abruptly but the drop in the dia phragm is slowed by restrictions at the bleed port and in the vacuum passage to the diaphragm lt e M a p A 1 J s s 4 Fig 7 Diaphragm slows air valve opening DASHPOT ACTION CONTROLS VALVE As the vacuum bleeds off the choke diaphragm acts as a dashpot preventing the secondary air valve from opening too quickly As a result in coming air flow opens the air valve at a rate which provides smooth pickup of the secondary discharge nozzle operation Accelerator Pump Operation The Thermo Ouad accelerator pump cylinder is part of the bowl cover casting and connects to its discharge jet in the primary section through a short flexible tube The intake check valve assembly acts as a bottom closure for the pump cylinder 4 hae am A Ti PED hd iY N I Ef o O n EC T A P M E t AT 4 i Ne 2 ue s F Fi 4 Fi l E M J gt p Ta b gt T ae a aa EAD c APT da gt pm a u d yee ba E 4 A q re r i e A E a
13. milar carburetors both valves in the Thermo Quad carburetor are linked to the choke vacuum kick diaphragm CHOKE DIAPHRAGM DOES DUAL DUTY In this case the choke diaphragm does two jobs Besides its regular vacuum kick function the dia phragm also restrains the air valve to keep it from opening too quickly If the air valve opens before adequate flow begins at the secondary nozzles flat spots can result SEPARATE SETTINGS NEEDED Because the choke diaphragm has two distinct functions separate adjustments must be made to set the air valve control and the vacuum kick Since these adjustments are inter related they must be made in the sequence described in this book and the Service Manuals THROTTLE BODY HOUSES CAM AND LEVER The throttle body section forms the mounting flange of the carburetor and houses the primary and secondary throttle valves The step up piston cam and lever are also located in the throttle body SOLENOID DETERMINES IDLE SPEED A curb idle speed solenoid is mounted on the car buretor throttle body casting or on the intake manifold on the throttle lever side This solenoid maintains a relatively high idle speed when the en gine is running but retracts when the ignition is turned off so the throttle can close farther to pre vent after running SECONDARY THROTTLE PICKUP LEVER Fig 4 No secondary operation when choke is on As in other carburetors engine vacuum moves the choke diaph
14. mple there is less chance of flooding due to overheated fuel expansion when the engine is shut off espe cially in hot weather And a cooler running car buretor maintains a more constant air fuel mixture ratio in all operating ranges er T Nr pm Pw SA ig d Ms b X n eu E uu Y a AJ V E THREE LAYER ASSEMBLY Fig 1 Bow acts as heat barrier DESIGN LOWERS EXHAUST EMISSIONS Thermo Quad metering calibration is leaner be cause mixture enrichment is not needed to com pensate for fuel expansion power losses As a re sult exhaust emissions are reduced without seriously affecting engine performance AIR MIXES IN AT DISCHARGE The 72 Thermo Quad has a conventional venturi throated primary section and straight bore air valve type secondaries In operation the metering system feeds the primary and secondary discharge nozzles with a solid continuous stream of fuel which mixes with air after it leaves the nozzles This differs from 71 Thermo Quads and other car buretors with conventional air bleed metering systems which introduce the air into the fuel stream before discharge from the nozzles PRIMARY METERING HAS MANUAL CONTROL Primary fuel flow is controlled by two metering rods yoked to a single vacuum operated step up piston which reacts basically to engine loading During the primary operation phase the step up piston and the metering rods are raised mechanical ly by a cam and lever ar
15. n equipment not available in service Tampering with the setting will upset performance and emission control so it should not be disturbed THERMO QUAD ADJUSTMENTS Before you touch any carburetor adjustment first check out all other possible trouble sources Then if linkage adjustments are needed make them in the proper sequence so one adjustment does not undo preceding ones Nearly all Thermo Quad adjustments can be made on or off the engine However the carburetor must be removed to check or adjust the secondary throttle link Fast idle speed curb idle speed and bowl vent valve settings are adjusted with the car buretor installed To cover the Thermo Quad adjustments we ll de scribe each external setting in the order recom mended for a complete checkout Adjustments which can be made separately are indicated In general adjustments which require bending must be made in sequence THERMO QUAD ADJUSTMENT SEQUENCE SECONDARY THROTTLE LINK SECONDARY AIR VALVE OPENING AIR VALVE SPRING TENSION ACCELERATOR PUMP STROKE CHOKE CONTROL LEVER CHOKE DIAPHRAGM ROD VACUUM KICK FAST IDLE CAM amp LINKAGE CHOKE UNLOADER SECONDARY THROTTLE PICKUP LEVER FAST IDLE SPEED CURB IDLE SPEED BOWL VENT VALVE Secondary Throttle Link To check the secondary throttle link setting the choke valve must first be blocked open This lowers the outer tang on the fast idle operating lever so the secondary throttle pickup lever moves
16. r valve to drop open SECONDARY AIR VALVE SPRING TENSION ADJUSTMENT MR VALVE STOP oe CONTACTS STOP LIGHTLY Fig 19 Tighten lock plug to hold spring setting THE TOOL IS HOLLOW Insert a screwdriver blade through the special tool and bring the air valve back up with initial spring windup tension until the valve lip contacts its clos ing stop lightly To do this you turn the adjust ment plug counterclockwise gradually as you test for light closing contact by applying repeated opening pressure on the air valve WIND UP THE SPRING From the initial air valve closing position continue to turn the adjusting plug the specified number of turns in the windup position At this point tighten the hollow lock plug with the special tool to hold the adjustment secure TION 13 PR Stroke The basic accelerator pump stroke adjustment pro cedure is the same on all Thermo Quads Begin with the choke valve wide open and the fast idle cam in the off position Then turn out the throttle stop screw so the throttle valves can close com pletely Also make sure that the hooked end of the x A Fw m p m TOP OF PLUNGER tom Us BOY OPEN ACCELERATOR PUMP STROKE ADJUSTMENT v im FAST IDLE CAM OFF BACK OFF E larly te GURB IDLE SCREW 2 gt 4 BEND THROTTLE Jm Pvt X CONNECTOR ROD All Dva p BEND PICKUP ARM by gaon ar os m e A s Ht Fig 20 Check s
17. ragm inward to produce vacuum kick action However the Thermo Ouad diaphragm stem is linked directly to the secondary air valve shaft lever by a connecting rod which also picks up the choke adjusting lever This pickup action pro duces the vacuum kick opening of the choke valve SECONDARIES STAY CLOSED While the engine is warming up with the choke on a tang on the fast idle operating lever lifts the sec ondary throttle pickup lever and disengages the secondary throttle linkage This prevents the sec ondary throttle valves from opening when the choke is on even if the pedal is floored s LEVER ENGAGES WHEN LINKAGE E MOVES TO OFF We S a 1 ES D KENS lt Fig 5 Lever picks up secondary linkage PICKUP LEVER ENGAGES LINKAGE The secondary throttle pickup lever drops and en gages the throttle linkage when the fast idle linkage moves to its off position The secondary throttle valves can then open in a normal manner but as long as these valves are closed the choke dia phragm holds the secondary air valve closed PASSAGE IS OPEN TO MANIFOLD Vacuum is routed to the choke diaphragm through a passage which connects to a chamber in the bottom of the throttle body This chamber is open to manifold vacuum regardless of throttle position VACUUM BLEED PASSAGE ALSO USED In addition a bleed passage extends from the dia phragm vacuum passage to a small port in the sec ondary bore on the choke diaphragm s
18. rangement which will be described farther on CHOKE DISCONNECTS SECONDARIES The secondary throttle valves are mechanically linked to the primaries and begin to open at ap proximately 70 m p h During the choking phase a pickup lever disengages to keep the secondary throttle valves from opening When the choke opens and the fast idle linkage moves to off posi tion the pickup lever drops into position where it engages the secondary throttle linkage to open the throttle valves SECONDARY METERING IS CONVENTIONAL Secondary fuel flow is metered by conventional jets connected to discharge nozzles which begin de livery when the secondary throttle valves start to ES PRIMARY VENTURIS ACCELERATOR PUMP STEP UP PISTON SECONDARY JETS BET RODS SECONDARY NOZZLES a I Og Fig 2 Cover includes metering components open As already mentioned the fuel discharges in a solid stream which mixes with air after leaving the nozzles BOWL COVER CARRIES METERING PARTS Float and needle valve assemblies primary dis charge nozzles and venturis accelerator pump and jet step up piston and metering rods and the sec ondary jets and nozzles are all part of the bowl cover assembly Two primary metering jets and a baffle plate are the only parts located in the plastic fuel bowl VALVES ARE LINKED TO DIAPHRAGM The bowl cover also houses a conventional choke valve and a spring loaded secondary air valve How ever unlike si
19. tion permits maximum inlet air flow through the carburetor to overcome flooding we check the setting with the throttle in the wide open position 4 CHOKE t UNLOADER L e ADIUSTNENT CHECK VALVE open THROTTLE X A 54 te a i ada WIDE gt ha a lad f OPEN EV RT WC m j gt BEND UNLOADER TANG Fig 29 Throttle must be wide open af FI AGA p Fs mE p E 1 ARIA T si BN Wu Eun Ts Lo 8 1 M XN A NANO X Xu En s les u BEYWF EB X IE E X A Here again we apply light closing force on the choke control lever and measure the amount that the choke valve opens A light drag as the drill or gauge is removed is okay Bend the unloader tang on the fast idle operating lever to adjust rk l 1 lar CK Up Lever s oh hee lam 3 JV 11TULLIE gt The secondary throttle pickup lever adjustment wraps up the settings which can be made with the carburetor off the car To check the lever setting you hold the choke control lever in the open choke position allowing the throttle pickup lever to drop and then measure the clearance between the pick up lever and its stop Bend the outer tang on the fast idle operating lever to adjust the clearance SECONDARY PICKUP ada t ADJUS TMENT ate n za BETWEEN LEVER AND S A gt Earlier we set the fast idle cam and linkage so now we re ready for the fast idle speed adjustment which can be made out of sequence The
20. tom surface of the float at the outer corner DO NOT BEND FLOAT LIP To adjust float height bend the float lever at the flat section near the lip end Lift the float when adjusting so the lip on the float lever does not press against the needle valve If the lip is distorted the float can hang up m z es b a a MH i n i UU LA I o M m k mn at _ M 2 8 Ze S B as is m gd et E oed M c K um e ae UR www carburetor manual com To prevent damage the metering rods should be installed after the carburetor sections are assem bled Position the upper rod ends inward in the ends of the step up piston yoke and carefully in stall as an assembly to prevent bending the rods or yoke ends CHECK BOTH SEALS Before you install the bowl cover make sure the O ring seals are in place in both primary nozzle wells If either or both seals are left out fuel will bypass the metering system and cause an over rich driving mixture MAKE SURE 0 RINGS ARE IN PLACE Fig 35 Omitted ring causes over rich mixture USE THE RIGHT SPRING The vacuum kick modulating spring used with car buretors on TorqueFlite models is colored for iden tification The manual transmission model spring has a dif
21. ust touches its stop Then back it out one full turn to make the final setting Bowl Vent Valve The final external Thermo Quad setting is the bowl vent valve adjustment which must be made after curb idle speed is set First remove the checking hole plug from the bowl cover and set the throttle at the curb idle position with the curb idle solenoid core extended ADJUSTMENT HE Y a my iE IL fj s TD BEND AT NOTCH AT CURB IDLE POSITION Fig 33 Contact vent valve lightly READ SETTING ON SCALE To measure the vent valve setting insert a narrow scale into the checking hole to make light contact with the spring loaded valve Bend the vent oper ating lever at the notch if adjustment is necessary After checking the valve opening install a new plug in the bowl cover checking hole Float Height Setting Although float height setting is not an external ad justment it is the only remaining Thermo Quad adjustment not covered so we ll describe it here If the floats are removed they should be replaced in their original locations Also make sure that both floats are free to move up and down without rub bing on the fuel bowl walls FLOAT HEIGHT ADJUSTMENT BEND ARM AT FLAT SECTION Fig 34 Measure at outer corner of float CHECK VERTICAL DIMENSION You check float height with the bowl cover invert ed so the floats can rest on their needle valves Make the measurement from the gasket to the bot
22. vent damage to the vertical vent tubes or the exposed step up piston yoke Slight bending or distortion at the yoke ends can result in binding especially with the piston in the raised position
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